The invention relates to a method for advancing a specimen or a cutting knife, by means of an advancing carriage, into a sectioning plane of a microtome, in particular into the sectioning plane of a disk microtome, in which the advancing carriage is moved by means of a motor drive.
A disk microtome is known from WO 98 04 898 A1. To carry out the sectioning, the disk microtome described in this document has a motor drive which is used to produce a relative movement between the object and the cutting knife. Furthermore, the disk microtome is equipped with a motor advancing device for setting the section thickness. Both adjustment motors may be designed as stepper motors and are connected to a control circuit. The motors are controlled by means of the control circuit. An angle-position encoder is provided in the disk microtome for the purpose of detecting the specimen position.
This document leaves open the question of the extent to which the specimen can be advanced substantially automatically into the sectioning plane.
Therefore, the object of the present invention is to refine a method for advancing a specimen or a cutting knife into the sectioning plane of a microtome in such a way that the specimen is substantially automatically positioned in the sectioning plane.
The method for advancing a specimen or a cutting knife, by means of an advancing carriage, into a sectioning plane of a microtome is distinguished by the fact that the advancing carriage is moved by means of a motor drive and the advancing carriage is initially advanced onto an area sensor. The drive used may, for example, be stepper motors or linear motors with incremental encoder.
When the specimen surface comes into contact with the area sensor, the position of the motor drive is determined and is compared with a stored position of the sectioning plane. Control signals for the motor drive are calculated from the two values, and the advancing carriage is advanced into the sectioning plane by the motor drive, taking these control signals into account.
In a further refinement of the method, to establish the location of the sectioning plane with respect to the location of the area sensor, the advancing carriage is advanced into the sectioning plane under manual control by means of the motor drive. When contact occurs between the specimen surface and the cutting knife, this position of the motor drive is determined. Then the advancing carriage is advanced onto the area sensor by the motor drive and, when the specimen surface comes into contact with the area sensor, the position of the motor drive is determined. The difference between the determined position of the motor drive when it has been advanced into the sectioning plane and the determined position of the advancing carriage when it has been advanced onto the area sensor is formed and stored as the positional value of the sectioning plane. However, it is also possible for the values stored to be not the difference between the two positions, but rather only the position of the sectioning plane, or both positions. It is merely necessary to ensure that the displacement distance for the motor drive from the sensor surface to the sectioning plane can be calculated.
In a further refinement of the invention, while the specimen is being advanced into the sectioning plane by the motor drive, the distance between the stored position of the sectioning plane and the position of the motor drive is determined continuously.
Also, the speed of the motor drive is regulated as a function of the determined distance between the stored position of the sectioning plane and the position of the motor drive. This ensures that the speed of the drive is reduced as the distances between the specimen and the sensor or the sectioning plane become shorter. This may take place continuously or in steps. This ensures that the drive is reliably decelerated in good time before the corresponding position is reached, so that it is prevented from running on, leading to an uncontrolled collision.
In a further refinement of the method, the continuously determined positions of the motor drive are compared with stored positions and, discrete positions coinciding, the speed of the motor drive is reduced and/or the force of the motor-adjustable parameter is increased.
In a further configuration of the invention, the location of the surface of the specimen which is to be sectioned is determined when it comes into contact with the surface of the sensor, and the difference from a stored value for the location of the sectioning plane is formed. By determining the position of the specimen surface, it is possible to achieve automatic alignment, preferably of a specimen which has already been sectioned or a specimen with a smooth surface. This prevents a specimen from being positioned and cut in an inclined position in the sectioning plane.
For this purpose, the specimen surface is aligned with respect to the area sensor by means of a motor-adjustable specimen holder and, in the process, three corners of the specimen successively come into contact with the sensor, and the three-dimensional location of the specimen is calculated from the three positions. Therefore, three corners of the specimen are successively brought into contact with the area sensor and, in the process, the corresponding position of the motor advancing-carriage drive and the positions of the motor-adjustable specimen holder are determined. From these positions, it is then possible to calculate and set a parallel position for the specimen surface with respect to the sectioning plane or the sensor surface.
Naturally, it is also possible for the values for the motor advancing carriage and the stepper motors of the specimen holder to be altered until there is no longer any contact signaled by the area sensor.
In a further configuration, the difference between the three-dimensional location of the specimen and a stored location is calculated, and the motor-adjustable specimen holder is activated as a function of the difference determined.